The compound 2,6-bis-(diethanolamino)-4,8-dipiperidinopyrimido[5,4-d]pyrimidine, known as dipyridamole, is disclosed in U.S. Pat. No. 3,031,450, incorporated herein by reference. This compound has been successfully used as an active substance, such as a coronary vasodilator, for many years. The pharmaceutical preparations previously known which contain this active substance have a number of disadvantages for certain applications due to the special physical properties of dipyridamole.
Dipyridamole is readily water-soluble only in an acidic medium, and therefore it can only go into solution from solid pharmaceutical forms and then be absorbed if the pharmaceutical preparations remain in the acidic range for a sufficiently long period. Thus, the solubility and hence also the absorption greatly depend upon the retention time and the pH value in the stomach and upper intestinal tract. This results in sharp inter-individual and intra-individual fluctuations in the blood levels (see Table 3 below) since the motility of a patent, the pH of the patient's stomach and intestines, and the patient's food intake have a considerable influence on absorption. In some patients the blood levels may even be so low that they practically amount to an absence of absorption.